Processing aids for use in manufacturing extruded polystyrene foams using low global warming potential blowing agents

ABSTRACT

A foamable polymeric mixture is provided that includes a polymer composition and at least one blowing agent. The blowing agent may comprise any blowing agents known not to deplete the ozone or increase the prevalence of global warming, such as CO 2 , HFO, HFC and mixtures thereof. The foamable polymeric mixture may further includes at least one processing aid comprising an organic phase changing material. The inventive foamable mixture is capable of processing at a pressure range of 800 to 1200 psi (5.5 to 8.3 MPa).

RELATED APPLICATIONS

This application claims priority from provisional application No.61/786,965 filed on Mar. 15, 2013, titled “Processing Aids for Use inManufacturing Extruded Polystyrene Foams Using Low Global WarmingPotential Blowing Agents.” Provisional application No. 61/786,965 isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to processes for forming polymeric foams andparticularly to the manufacture of extruded polystyrene (XPS) foams inthe absence of blowing agents that are known to deplete the ozone andincrease the prevalence of global warming. This invention provides theuse of a novel processing aid to stabalize the XPS foaming extrusionprocess and increase the operating window of XPS foam manufacturing.

BACKGROUND

The general procedure utilized in the preparation of extruded syntheticfoam bodies generally includes the steps of melting a base polymericcomposition, incorporating one or more blowing agents and otheradditives into the polymeric melt under conditions that provide for thethorough mixing of the blowing agent and the polymer while preventingthe mixture from foaming prematurely, e.g., under pressure. This mixtureis then typically extruded through a single or multi-stage extrusion dieto cool and reduce the pressure on the mixture, allowing the mixture tofoam and produce a foamed product. As will be appreciated, the relativequantities of the polymer(s), blowing agent(s) and additives, thetemperature and the manner in which the pressure is reduced will tend toaffect the qualities and properties of the resulting foam product. Aswill also be appreciated, the foamable mixture is maintained under arelatively high pressure until it passes through an extrusion die and isallowed to expand in a region of reduced pressure. Although reducedrelative to the pressure at the extrusion die, the reduced pressureregion may actually be maintained at a pressure above atmosphericpressure, for example up to about 2 atm or even more in someapplications, may be maintained at a pressure below atmosphericpressure, for example down to about 0.25 atm or even less in someapplications. Further, unless indicated otherwise, all references topressure provided herein are stated as the absolute pressure.

The solubility of conventional blowing agents, such aschlorofluorocarbons (“CFCs”) and certain alkanes, in polystyrene tendsto reduce the extrusion melt viscosity and improve cooling of expandedpolystyrene melts. For example, the combination of pentane and a CFCssuch as Freon 11 and 12 is partially soluble in polystyrene and has beenused for generating polystyrene foams that exhibited a generallyacceptable appearance and physical properties such as surface finish,cell size and distribution, orientation, shrinkage and stiffness.

However, in response to the apparent contribution of such CFC compoundsto the reduction of the ozone layer in Earth's stratosphere, thewidespread use and accompanying atmospheric release of such compounds inapplications such as aerosol propellants, refrigerants, foam-blowingagents and specialty solvents has recently been drastically reduced oreliminated by government regulation.

The divergence away from the use of CFCs has led to utilization ofalternative blowing agents, such as hydrogen-containingchlorofluoroalkanes (HCFCs). However, while HCFC's are considered to beenvironmentally friendly blowing agents compared to CFCs, such compoundsdo still contain some chlorine and are therefore said to have an ozonedepletion potential.

Another alternative class of blowing agents, hydrofluorocarbons (HFC's),are now being commonly used as more ozone friendly options.Particularly, CF₃CH₂CF₂H (HFC-245fa), 1,1,1,2-tetrafluoroethane(HFC-134a) and 1,1-difluoroethane (HFC-152a), offer desirableimprovements, such as improved insulation, due at least in part to thelow thermal conductivity of the vapor.

Hydrocarbons such as pentane, hexane, cyclopentane and other homologs ofthis series have also been considered.

A new generation of fluroralkene blowing agents have been developed withlow ODP (ozone depletion potential) and low GWP (global warmingpotential) known as hydroflouroolefins (HFOs). HFOs have been identifiedas potential low global warming potential blowing agents for theproduction of thermoplastic foams, such as polystyrene foam, for thermalinsulation.

BRIEF SUMMARY

The general inventive concepts are directed to a foamable polymericmixture. The foamable polymeric mixture comprises a polymer composition,such as a polystyrenic composition and at least one blowing agent. Theblowing agent may comprise any blowing agents known not to deplete theozone or increase the prevalence of global warming. Such blowing agentsmay consist of, for example, carbon dioxide, hydrofluoroolefins, andhydrofluorocarbons, along with mixtures thereof. The foamable polymericmixture may further includes at least one processing aid comprising anorganic phase changing material. The inventive foamable mixture iscapable of processing at a pressure range of 800 to 1200 psi (5.5 to 8.3MPa).

The general incentive concepts further relate to a method ofmanufacturing extruded polymeric foam. The method includes introducing apolymeric composition into a screw extruder to form a polymer melt andinjecting at least one organic phase changing processing aid and atleast one blowing agent into the polymer melt to form an foamablepolymeric material. The blowing agent preferably comprises one or morelow ozone depletion and low global warming potential compounds, such ascarbon dioxide, hydrofluorocarbon, hydrofluoroolefin, and mixturesthereof. The method further includes extruding the foamable polymericcomposition through a die under a processing temperature between 800 and1200 psi (5.5 to 8.3 MPa) to produce a polymeric foam.

Further inventive concepts relate to an extruded polymeric foam. Theextruded polymeric foam is formed from a foamable polymer material thatincludes a polymeric composition, at least one blowing agent, and anorganic phase changing processing aid. The blowing agent may include oneor more of carbon dioxide, hydrofluoroolefin, hydrofluorocarbon, andmixtures thereof. The processing aid may comprise an organic phasechanging material. It is an object of the present invention that whereinsaid foam has an R-value between 4 and 7 per inch.

Additional inventive aspects relate to a foamable polymeric mixture thatincludes a polymer composition, at least one blowing agent, and at leastone processing aid. The blowing agent comprising at least one of carbondioxide, hydrofluoroolefins, and hydrofluorocarbons, and mixturesthereof. The processing aid may include an organic phase changingmaterial. The foamable polymeric mixture is capable of forming anextruded polymeric foam having the following properties: an R-valuebetween 4 and 7 per inch, an average cell size between 0.005 and 0.6 mm,a compressive strength between 6 and 80 psi, a density between 1.3-4pcf; and an open cell content of less than 30 percent.

The foregoing and other objects, features, and advantages of the generalinventive concepts will become more readily apparent from aconsideration of the detailed description that follows.

DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will be apparent from the moreparticular description of certain example embodiments of the inventionprovided below and as illustrated in the accompanying drawings.

FIG. 1 is a schematic drawing of an exemplary extrusion apparatus usefulfor practicing methods according to the invention.

FIG. 2 is a graph depicting a DSC curve of an exemplary phase changingprocessing aid.

FIG. 3 is a graphical depiction of the main effects from polystyrenemelt flow index, CO₂ concentration, and phase changing processing aidshave on density.

FIG. 4 is a graphical depiction of the main effects from polystyrenemelt flow index, CO₂ concentration, and phase changing processing aidshave on foam cell size.

FIG. 5 is a graphical depiction of the main effects from polystyrenemelt flow index, CO₂ concentration, and phase changing processing aidshave on foam compressive strength.

DETAILED DESCRIPTION

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which the invention belongs. Although any methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present invention, the preferred methodsand materials are described herein. All references cited herein,including published or corresponding U.S. or foreign patentapplications, issued U.S. or foreign patents, or any other references,are each incorporated by reference in their entireties, including alldata, tables, figures, and text presented in the cited references. Inthe drawings, the thickness of the lines, layers, and regions may beexaggerated for clarity. It is to be noted that like numbers foundthroughout the figures denote like elements. The terms “composition” and“inventive composition” may be used interchangeably herein.

As used herein, the term “blowing agent” is understood to includephysical (e.g., dissolved gaseous agents) or chemical blowing agents(e.g., a gas generated by decomposition). A blowing agent is generallyadded to a molten polymer, e.g., in an extruder, and under the properconditions, to initiate foaming to produce a foamed thermoplastic. Theblowing agent expands the resin and forms cells (e.g., open or closedpores). As the resin hardens or cures a foam is produced with either theblowing agent trapped in the cells or ambient air displaces the blowingagent in the cells. The blowing agents discussed herein are preferred tobe environmentally acceptable blowing agents (e.g., they are generallysafe for the environment) as would be recognized by one of ordinaryskill in the art.

As used herein, unless specified otherwise, the values of theconstituents or components of the blowing agent or other compositionsare expressed in weight percent or % by weight of each ingredient in thecomposition. The values provided include up to and including theendpoints given.

The present invention relates to a polymeric foam and polymeric foamproducts, such as extruded or expanded polystyrene foams, formed from acomposition that contains a foamable polymer material, at least oneblowing agent (for example, hydrofluorocarbons (HFCs).hydrofluoroolefins (HFOs), and/or carbon dioxide (CO₂)), and aprocessing aid. The present invention further relates to a method formanufacturing such a polymeric foam or foam product. In some exemplaryembodiments, the processing aid makes it possible to employ blowingagents, such as CO₂, HFO and HFC, which have low global warmingpotential and low ozone depletion potential, to make polymeric, closedcell foam under traditional processing conditions.

FIG. 1 illustrates a traditional extrusion apparatus 100 useful forpracticing methods according to the present invention. The extrusionapparatus 100 may comprise a single or double (not shown) screw extruderincluding a barrel 102 surrounding a screw 104 on which a spiral flight106 is provided, configured to compress, and thereby, heat materialintroduced into the screw extruder. As illustrated in FIG. 1, thepolymeric composition may be feed into the screw extruder as a flowablesolid, such as beads, granules or pellets, or as a liquid or semi-liquidmelt, from one or more (not shown) feed hoppers 108.

The foamable polymer composition is the backbone of the formulation andprovides strength, flexibility, toughness, and durability to the finalproduct. The foamable polymer composition is not particularly limited,and generally, any polymer capable of being foamed may be used as thefoamable polymer in the resin mixture. The foamable polymer compositionmay be thermoplastic or thermoset. The particular polymer compositionmay be selected to provide sufficient mechanical strength and/or to theprocess utilized to form final foamed polymer products. In addition, thefoamable polymer composition is preferably chemically stable, that is,generally non-reactive, within the expected temperature range duringformation and subsequent use in a polymeric foam. Non-limiting examplesof suitable foamable polymer compositions include at least one of thefollowing materials: alkenyl aromatic polymers, polyvinyl chloride(PVC), chlorinated polyvinyl chloride (CPVC), polyethylene,polypropylene, polycarbonates, polyisocyanurates, polyetherimides,polyamides, polyesters, polycarbonates, polymethylmethacrylate,polyurethanes, phenolics, polyolefins, styreneacrylonitrile (SAN),acrylonitrile butadiene styrene, acrylic/styrene/acrylonitrile blockterpolymer (ASA), polysulfone, polyurethane, polyphenylenesulfide,acetal resins, polyamides, polyaramides, polyimides, polyacrylic acidesters, copolymers of ethylene and propylene, copolymers of styrene andbutadiene, copolymers of vinylacetate and ethylene, rubber modifiedpolymers, thermoplastic polymer blends, and combinations thereof.

In one exemplary embodiment, the foamable polymer composition is analkenyl aromatic polymer material. Suitable alkenyl aromatic polymermaterials include alkenyl aromatic homopolymers and copolymers ofalkenyl aromatic compounds and copolymerizable ethylenically unsaturatedco-monomers. In addition, the alkenyl aromatic polymer material mayinclude minor proportions of non-alkenyl aromatic polymers. The alkenylaromatic polymer material may be formed of one or more alkenyl aromatichomopolymers, one or more alkenyl aromatic copolymers, a blend of one ormore of each of alkenyl aromatic homopolymers and copolymers, or blendsthereof with a non-alkenyl aromatic polymer.

Examples of alkenyl aromatic polymers include, but are not limited to,those alkenyl aromatic polymers derived from alkenyl aromatic compoundssuch as styrene, alpha-methyistyrene, ethylstyrene, vinyl benzene, vinyltoluene, chlorostyrene, and bromostyrene. In at least one embodiment,the alkenyl aromatic polymer is polystyrene.

It is to be appreciated that the properties of the extruded foam or foamproduct may be modified by the selection of the molecular weight of thepolymer. For example, the preparation of lower density extruded foamproducts is facilitated by using lower molecular weight polymers. On theother hand, the preparation of higher density extruded foam products isfacilitated by the use of higher molecular weight polymers or higherviscosity resins.

As the polymeric composition advances through the screw extruder 100,the decreasing spacing of the flight 106, defines a successively smallerspace through which the polymer composition is forced by the rotation ofthe screw. This decreasing volume acts to increase the temperature ofthe polymer composition to obtain a polymeric melt (if solid startingmaterial was used) and/or to increase the temperature of the polymericmelt.

In some exemplary embodiments, one or more polymer processing aidsand/or blowing agents may be provided through the feed hopper 108. Inother exemplary embodiments, as the polymer composition advances throughthe screw extruder 100, one or more ports may be provided through thebarrel 102 with associated apparatus 110 configured for injecting one ormore polymer processing aids into the polymer composition. Similarly,one or more ports may be provided through the barrel 102 with associatedapparatus 112 for injecting one or more blowing agents into the polymercomposition.

Exemplary methods according to the invention may utilize one or more ofa variety of blowing agents to achieve the desired polymeric foamproperties in the final product. According to one aspect of the presentinvention, the blowing agent composition comprises one or more of CO₂and halogenated blowing agents, such as hydrofluorocarbons (HFCs),hydrochlorofluorocarbons, hydrofluoroethers, hydrofluoroolefins (HFOs),hydrochlorofluoroolefins, hydrobromofluoroolefins, hydrofluoroketones,hydrochloroolefins, and fluoroiodocarbons, alkyl esters, such as methylformate, water, and mixtures thereof. In other exemplary embodiments,the blowing agent comprises one or more of CO₂, HFOs, HFCs, and mixturesthereof.

The blowing agent may be introduced in liquid or gaseous form (e.g., aphysical blowing agent) or may be generated in situ while producing thefoam (e.g., a chemical blowing agent). For instance, the blowing agentmay be formed by decomposition of another constituent during productionof the foamed thermoplastic. For example, in the case of a blowing agentthat comprises CO₂, a carbonate composition or polycarbonic acid may beadded to the foamable resin and carbon dioxide will be generated uponheating during the extrusion process. In some exemplary embodiments, CO₂is included as a blowing agent in an amount from about 0.05 to 5.0weight percent. In other exemplary embodiments, CO₂ is included in anamount between about 1.0 and 3.5 weight percent.

The blowing agent may further comprise one or more hydrofluoroolefinblowing agents, such as for example, 3,3,3-trifluoropropene(HFO-1243zf); 2,3,3-trifluoropropene; (cis and/ortrans)-1,3,3,3-tetrafluoropropene (HFO-1234ze), particularly the transisomer; 1,1,3,3-tetrafluoropropene; 2,3,3,3 -tetrafluoropropene(HFO-1234yf); (cis and/or trans)-1,2,3,3,3-pentafluoropropene(HFO-1225ye); 1,1,3,3,3 -pentafluoropropene (HFO-1225zc); 1,1,2,3,3-pentafluoropropene (HFO-1225yc); hexafluoropropene (HFO-1216);2-fluoropropene, 1-fluoropropene; 1,1-difluoropropene;3,3-difluoropropene; 4,4,4-trifluoro-1-butene;2,4,4,4-tetrafluorobutene-1; 3,4,4,4-tetrafluoro-1-butene;octafluoro-2-pentene (HFO-1438);1,1,3,3,3-pentafluoro-2-methyl-1-propene; octafluoro-1-butene;2,3,3,4,4,4-hexafluoro-1-butene; 1,1,1,4,4,4-hexafluoro-2-butene(HFO-1336m/z); 1,2-difluoroethene (HFO-1132);1,1,1,2,4,4,4-heptafluoro-2-butene; 3-fluoropropene,2,3-difluoropropene; 1,1,3-trifluoropropene; 1,3,3-trifluoropropene;1,1,2-trifluoropropene; 1-fluorobutene; 2-fluorobutene;2-fluoro-2-butene; 1,1-difluoro-1-butene; 3,3-difluoro-1-butene;3,4,4-trifluoro-1-butene; 2,3,3-trifluoro-1-butene;1,1,3,3-tetrafluoro-1-butene; 1,4,4,4-tetrafluoro-1-butene;3,3,4,4-tetrafluoro-1-butene; 4,4-difluoro-1-butene;1,1,1-trifluoro-2-butene; 2,4,4,4-tetrafluoro-1-butene;1,1,1,2-tetrafluoro-2 butene; 1,1,4,4,4-pentafluorol-butene;2,3,3,4,4-pentafluoro-1-butene; 1,2,3,3,4,4,4-heptafluoro-1-butene;1,1,2,3,4,4,4-heptafluoro-1-butene; and1,3,3,3-tetrafluoro-2-(trifluoromethyl)-propene.

In some exemplary embodiments, the blowing agent may comprise one ormore hydrofluorocarbons. The specific hydrofluorocarbon utilized is notparticularly limited. A non-exhaustive list of examples of suitableblowing HFC blowing agents include 1,1-difluoroethane (HFC-152a),1,1,1,2-tetrafluoroethane (HFC-134a), 1,1,1-trifluoroethane (HFC-143a),difluoromethane (HFC-32), 1,3,3,3-pentafluoropropane (HFO-1234ze),pentafluoro-ethane (HFC-125), fluoroethane (HFC-161),1,1,2,2,3,3-hexafluoropropane (HFC 236ca), 1,1,1,2,3,3-hexafluoropropane(HFC-236ea), 1,1,1,3,3,3-hexafluoropropane (HFC-236fa),1,1,1,2,2,3-hexafluoropropane (HFC-245ca), 1,1,2,3,3-pentafluoropropane(HFC-245ea), 1,1,1,2,3 pentafluoropropane (HFC-245eb),1,1,1,3,3-pentafluoropropane (HFC-245fa), 1,1,1,4,4,4-hexafluorobutane(HFC-356mff), 1,1,1,3,3 -pentafluorobutane (HFC-365mfc), andcombinations thereof.

In some exemplary embodiments, the HFOs and/or HFCs may be included as ablowing agent in an amount from about 0.05 to 5.0 weight percent. Inother exemplary embodiments, the HFOs and/or HFCs is included in anamount between about 2.0 and 4.0 weight percent.

In addition to the blowing agents, one or more processing aids may beadded to the polymeric melt to increase the processing window for thepolystyrene foam manufacturing. In some exemplary embodiments, theprocessing aid(s) comprises an organic low molecular weight material,such as, for example a phase changing material. A phase changingmaterial is a material that has a transition temperature from liquid tosolid at a particular temperature. The transition temperature of thephase changing material may be varied in a wide temperature range (−40to 150° C.), depending on the different molecular chain lengths. In someexemplary embodiments, the phase changing material that has a transitiontemperature from liquid to solid at 24° C. (“PT 24”). The phase changingmaterial may comprise organic phase changing materials, such as, forexample, fatty acid esters and wax, or a combination of the two. In someexemplary embodiments, the organic phase changing material comprisesbetween about 16 and 18 carbons, such as an octyl ester of hexadecanoicacid, also known as synthetic beeswax.

The processing aid may be included in any amount to provide the requiredbenefit to the polystyrene foam process. In some exemplary embodiments,the processing aid is included in about 0.05 to about 10.0 weightpercent. In other exemplary embodiments, the processing aid is includedin an amount from about 0.5 to about 3.0 weight percent.

The fatty acid esters may be pumped directly into an extruder in theliquid form, or alternatively, the fatty acid esters may bemicroencapsulated into powders and fed directly into a hopper. Thematerial used to microencapsulate the fatty acid esters may comprise oneor more polymers, such as, for example, melamine formaldehyde, ureaformaldehyde, and acrylate copolymer resins. According to variousaspects of the present invention, microencapsulation of the fatty acidesters may reduce the diffusivity of blowing agents by trapping theblowing agent gases inside the microencapsulation shells. Such anencapsulation provides controlled release, wherein the shell may let CO₂diffuse in, but will keep the fatty acid ester from diffusing out of theshell. It is further contemplated that the fatty acid esters becompounded into a carrier material, such as a polystyrene polymermaterial, and incorporated into the masterbatch pellets for directdelivery into the extruder.

Exemplary phase changing materials may include the materials listedbelow in Table 1.

TABLE 1 Phase Changing Materials and corresponding phase transitiontemperatures. Phase transition temperatures from soilid to PCMs liquid(° C.) Chemical composition PT-5 −5 Synthetic Beeswax PT24 24 SyntheticBeeswax PT24 microencap- 24 80% Synthetic Beeswax sulated powder 20%encapsulated wall material PT33 microencap- 33 80% Synthetic Beeswaxsulated powder 20% encapsulated wall material PT60 60 Synthetic Beeswax

FIG. 2 illustrates a DSC curve of one exemplary phase changing material(PT24), in which the phase transition temperature from solid to liquidis determined as the peak value of 24.61° C.

Inclusion of a fatty acid ester processing aid(s) causes the windowavailable for processing to widen in various ways. For instance, thechemical structure of phase changing materials may make them morecompatible with blowing agents and thus increase the solubility of theblowing agents in polystyrene and decrease the diffusivity of the gasesout of the polystyrene. Additionally, the low molecular weight of thephase changing materials may plasticize the polystyrene melt and improvethe rheological properties for better foaming. The processing window mayfurther be widened due to the release of heat from the phase changingmaterials by changing from liquid to solid phase during foam boardcooling process, which may slow down the melt gelation (board settling)process. By widening the operating window, the foam is able to achievedesirable properties, such as a sufficient R value.

The foamable composition may further contain at least one infraredattenuating agent (IAA) to increase the R-value of the foam product.Blowing agents such as HFCs and HFOs, while environmentally friendly,tend to decrease the R-value of the foam product compared to aconventional HCFC foamed product. It was discovered, however, that theaddition of low levels of an infrared attenuating agent to a foamablecomposition containing such blowing agents may increase the R-value ofthe foam to an amount at least comparable to, or better than, a foamproduced with an HCFC blowing agent. Although the infrared attenuatingagent increases the R-value for foams that include HFO and/or HFCblowing agents, the addition of infrared attenuating agents also tendsto decrease the cell size of the cells in the foam, which results inundesirable final foamed products. In particular, small cell sizes tendto increase board bulk density, increase product cost, and reduce theprocess window during the extrusion process. Further, infraredattenuating agents undesirably increase the melt rheology, which willresult in an increase of the die pressure.

Non-limiting examples of suitable infrared attenuating agents for use inthe present composition include nanographite, carbon black, powderedamorphous carbon, asphalt, granulated asphalt, milled glass, fiber glassstrands, mica, black iron oxide, metal flakes (for example, aluminumflakes), carbon nanotube, nanographene platelets, carbon nanofiber,activated carbon, titanium dioxide, and combinations thereof. Inexemplary embodiments, the infrared attenuating agent is present in thefoam composition in an amount from 0.005% to 5.0% by weight of the totalcomposition. In other embodiments, the infrared attenuating agent may bepresent in an amount from 0.05 to 3.0% by weight, from 0.05 to 2.0% byweight, or from 0.1 to 1.0% by weight. In some exemplary embodiments,the infrared attenuating agent is present in the composition in anamount less than or equal to 0.5% by weight.

In at least one exemplary embodiment, the infrared attenuating agent isnanographite. The nanographite can be multilayered by furnace hightemperature expansion from acid-treated natural graphite or microwaveheating expansion from moisture saturated natural graphite. In addition,the nanographite may be a multi-layered nanographite which has at leastone dimension with a thickness less than 100 nm. In some exemplaryembodiments, the graphite may be mechanically treated such as by air jetmilling to pulverize the nanographite particles. The pulverization ofthe particles ensures that the nanographite flake and other dimensionsof the particles are less than 150 microns.

The nanographite may or may not be chemically or surface modified andmay be compounded in a polyethylene methyl acrylate copolymer (EMA),which is used both as a medium and a carrier for the nanographite. Otherpossible carriers for the nanographite include polymer carriers such as,but not limited to, polymethyl methacrylate (PMMA), polystyrene,polyvinyl alcohol (PVOH), and polyvinyl acetate (PVA). In exemplaryembodiments, the nanographite is substantially evenly distributedthroughout the foam. As used herein, the phrase “substantially evenlydistributed” is meant to indicate that the substance (for example,nanographite) is evenly distributed or nearly evenly distributed withinthe foam.

Further, the inventive composition may contain a fire retarding agent inan amount up to 1.0% by weight. For example, fire retardant chemicalsmay be added in the extruded foam manufacturing process to impart fireretardant characteristics to the extruded foam products. Non-limitingexamples of suitable fire retardant chemicals for use in the inventivecomposition include brominated aliphatic compounds such ashexabromocyclododecane and pentabromocyclohexane, brominated phenylethers, esters of tetrabromophthalic acid, and combinations thereof.

Optional additives such as nucleating agents, plasticizing agents,pigments, elastomers, extrusion aids, antioxidants, fillers, antistaticagents, biocides, and/or UV absorbers may be incorporated into theinventive composition. These optional additives may be included inamounts necessary to obtain desired characteristics of the foamable gelor resultant extruded foam products. The additives may be added to thepolymer mixture or they may be incorporated in the polymer mixturebefore, during, or after the polymerization process used to make thepolymer.

Once the polymer processing aid(s), blowing agent(s), and optionaladditional additives have been introduced into the polymeric material,the resulting mixture is subjected to some additional blendingsufficient to distribute each of the additives generally uniformlythroughout the polymer composition to obtain an extrusion composition.

This extrusion composition is then forced through an extrusion die 114and exits the die into a region of reduced pressure (which may be above,or more typically below atmospheric pressure), thereby allowing theblowing agent to expand and produce a polymeric foam layer or slab. Thepolymeric foam may be subjected to additional processing such ascalendaring, water immersion, cooling sprays or other operations tocontrol the thickness and other properties of the resulting polymericfoam product.

The foam composition produces rigid, substantially closed cell, polymerfoam boards prepared by an extruding process. Extruded foams have acellular structure with cells defined by cell membranes and struts.Struts are formed at the intersection of the cell membranes, with thecell membranes covering interconnecting cellular windows between thestruts. In the present invention, the inventive composition producessubstantially closed cellular foams with an average density of 1.0lbs/ft.³ to 5.0 lbs/ft.³, or from 1.3 lbs/ft.³-4.0 lbs/ft.³. It is to beappreciated that the phrase “substantially closed cell” is meant toindicate that the foam contains all closed cells or nearly all of thecells in the cellular structure are closed. In most exemplaryembodiments, not more than 30.0% of the cells are open cells, andparticularly, not more than 10.0%, or more than 5.0% are open cells, orotherwise “non-closed” cells. The closed cell structure helps toincrease the R-value of a formed, foamed insulation product. It is to beappreciated, however, that it is within the purview of the presentinvention to produce an open cell structure, although such an open cellstructure is not an exemplary embodiment.

Additionally, the inventive foam composition produces extruded foamsthat have insulation values (R-values) of about 4.0-7.0 per inch. In atleast one embodiment, the R-value 5.0 per inch. In addition, the averagecell size of the inventive foam and foamed products is 0.005 mm (5microns) to 0.6 mm (600 microns) and, in some embodiments, from 0.160 mm(160 microns) to 0.200 mm (200 microns). The extruded inventive foam maybe formed into an insulation product such as rigid insulation boards,insulation foam, packaging products, and building insulation orunderground insulation (for example, highway, airport runway, railway,and underground utility insulation).

The inventive foamable composition additionally may produce extrudedfoams that have a high compressive strength, which defines the capacityof a foam material to withstand axially directed pushing forces. In atleast one exemplary embodiment, the inventive foam compositions have acompressive strength within the desired range for extruded foams, whichis between about 6 and 80 psi. In some exemplary embodiments, theinventive foamable composition produces a foam having a compressivestrength between 20 and 68 psi.

In accordance with another exemplary aspect, the extruded inventivefoams possess a high level of dimensional stability. For example, thechange in dimension in any direction is 5% or less. In addition, thefoam formed by the inventive composition is desirably monomodal and thecells have a relatively uniform average cell size. As used herein, theaverage cell size is an average of the cell sizes as determined in theX, Y and Z directions. In particular, the “X” direction is the directionof extrusion, the “Y” direction is the cross machine direction, and the“Z” direction is the thickness. In the present invention, the highestimpact in cell enlargement is in the X and Y directions, which isdesirable from an orientation and R-value perspective. In addition,further process modifications would permit increasing the Z-orientationto improve mechanical properties while still achieving an acceptablethermal property. The extruded inventive foam can be used to makeinsulation products such as rigid insulation boards, insulation foam,and packaging products.

have been described above both generically and with regard to variousexemplary embodiments. Although the general inventive concepts have beenset forth in what is believed to be exemplary illustrative embodiments,a wide variety of alternatives known to those of skill in the art can beselected within the generic disclosure. Additionally, following examplesare meant to better illustrate the present invention, but do in no waylimit the general inventive concepts of the present invention.

EXAMPLES

The following examples introduce about 0.5˜3.0 wt % of phase changingprocessing aid materials into a polystyrene formulation to facilitateXPS foam board extrusion using a traditional extrusion processing line.The extrusion line had a production rate of 100˜160 kg/hr. The blowingagents used in the foam board extrusion process included CO₂ and/orHFO-1234ze. The process produced foam boards having a thickness of about1 inch and a width greater than 20 inches using a foaming dietemperature between 110 to 130° C. and a foaming die pressure between800 to 1100 psi.

Example 1 Operating Window Expansion with Phase Changing Materials inCO₂ Foaming

One percent of PT24 microencapsulated powder containing 80% phasechanging material and 20% encapsultion wall material was applied for XPSfoaming using about 3.7-4.3% CO₂ blowing agent. A foam board with a 1inch thickness was produced smoothly and the properties of the resultingfoam board are shown as Samples 1 & 2 in Table 2 below. The foam boardproperties are each within the acceptable range for traditional foamborads. Particulalry, the boards have a density between about 1.4 and 3psi, an R-value of 4-7 per inch. a cell size between about 0.005 and 0.6mm, a compressive strength between about 6 and 80 psi, and an open cellcontent of less than 30 percent. On the contrary, without the phasechanging material, the process could not be continued under the similarprocessing conditions due to the overshooting of die pressure (Sample#3). This observation indicates that phase changing materials arenecessary to balance the pressure profile in the XPS foaming extrusionline. This makes the phase changing material a necessary processing aidthat helps to operate the extrusion at significantly lower pressures.

TABLE 2 Application of PCM (PT microencapsulated powder) for CO₂ XPSfoaming. PT24 Die Foam Cell Compressive Sample microencapsulatedpressure density R size Open cell strength # powder (wt %) (psi) (pcf)value (mm) (%) (psi) 1 1 1072 2.71 4.29 0.182 3.39 36.09 2 1 1081 1.874.15 0.201 4.59 20.74 3 0 >1200 N/A N/A N/A N/A N/A

Example 2 Application of PT24 Liquid in CO₂ Foaming

A liquid processing aid, PT24, was injected directly into the extruderwith 3.5% CO₂ as the blowing agent. An XPS foam board with good surfacequality was produced without any modification to the traditional foamingconditions. The foam board properties are illustrated below, in Table 3.This further proves the benefit of using the subject phase changingmaterials as a processing aid when using CO₂ as the blowing agent.

TABLE 3 Application of PT24 liquid for CO₂ XPS foaming Foam CellCompressive Sample PT24 liquid density R size Open cell strength # (wt%) (pcf) value (mm) (%) (psi) 4 0.8 2.81 4.41 0.16 1.99 36.6 5 1.2 2.774.39 0.17 5.94 32.6 6 1.6 2.78 4.41 0.17 6.31 32.8

Example 3 Design of Experiment (DOE) of Using PT24 MicroencapsulatedPowder in CO₂ Foaming

A Design of Experiment (“DOE”) was developed to understand the influencethat phase changing processing aids have on foam properties. A DOE is aninformation gathering exercise where one or more variations are present.The particular DOE designed was based on three key parameters: phasechanging material usage level (between 1 and 3 weight %), polystyrenemelt flow index, and CO₂ concentration. A single DOE having threefactors and two levels (low and high) was performed.

The main effects from the three key parameters to foam density, foamcell size, and compressive strength are summarized in FIGS. 3, 4, & 5,respectively. FIG. 3 illustrates the effects the various parameters haveon foam density when exposed to both low and high levels. For instance,at a high polystyrene melt flow index, the foam density is also high.Conversely, as the CO₂ or phase changing material concentrationincreases, the foam density decreases. FIG. 4 illustrates the effectsthe various parameters have on cell size. Based on the DOE results, itappears that increasing the polystyrene melt flow also increases thefoam cell size; however, as was the case with density, increasing theCO₂ concentration lowers the cell size of the foam. The amount of phasechanging material does not seem to affect the foam cell size. Withregard to compression, FIG. 5 illustrates that a decreased polystyrenemelt flow index appears to also lower the foam compressive strength,while increasing the amount of phase changing material also lowers thefoam compressive strength. However, increasing the CO₂ concentrationseems to also increase the compressive strength.

Example 4 Application of PT24 Microencapsulated Powder on HFO-1234zeFoaming

Phase changing materials were shown to be good processing aids whenusing HFO and CO₂ as the blowing agents. Table 4, below, summarizes themanufactured foam board properties. Different levels of HFO-1234ze werecombined with different levels of CO₂. As a processing aid, 1.0 wt %PT24 microencapsulated powder was included. Although the cell size is onthe low end of traditional XPS foams, other properties are well withinthe acceptable range. Additionally, the process is more stable thanwithout phase changing materials as a processing aid.

TABLE 4 Application of PT24 microencapsulated powder for HFO/CO₂ XPSfoaming. PT24 HFO- Foam Cell Compressive Sample microencapsulated 1234zeCO2 density R size Open cell strength # powder (wt %) (wt %) (wt %)(pcf) value (mm) (%) (psi) 7 1 2.5 3.0 2.90 4.74 0.10 1.25 71.3 8 1 2.53.0 2.94 4.72 0.10 1.34 77.4 9 1 2.5 2.7 2.85 4.74 0.10 1.98 63.0 10 14.0 2.1 2.94 4.88 0.09 0.33 70.5 11 1 4.0 2.1 2.85 4.81 0.09 1.79 75.712 1 4.0 1.0 3.36 4.93 0.13 1.71 67.9

Although the present invention has been described with reference toparticular means, materials and embodiments, from the foregoingdescription, one skilled in the art can easily ascertain the essentialcharacteristics of the present invention and various changes andmodifications can be made to adapt the various uses and characteristicswithout departing from the spirit and scope of the present invention asdescribed above and set forth in the attached claims.

1. A foamable polymeric mixture comprising: a polymer composition; atleast one blowing agent, said blowing agent comprising at least one ofcarbon dioxide, hydrofluoroolefins, and hydrofluorocarbons, and mixturesthereof; and at least one processing aid comprising an organic phasechanging material, wherein said foamable mixture is capable ofprocessing at a pressure range of 800 to 1200 psi (5.5 to 8.3 MPa). 2.The foamable polymeric mixture of claim 1, wherein said polymercomposition comprises an alkenyl aromatic polymer.
 3. The foamablepolymeric mixture of claim 2, wherein said polymer composition comprisesa polystyrene.
 4. The foamable polymeric mixture of claim 1, whereinsaid foamable polymeric mixture comprises at least 0.05 to 5.0 weightpercent CO₂.
 5. The foamable polymeric mixture of claim 1, wherein saidprocessing aid comprises at least one of a fatty acid ester and a wax.6. The foamable polymeric mixture of claim 5, wherein said processingaid comprises a synthetic beeswax.
 7. The foamable polymeric mixture ofclaim 1, wherein said processing aid comprises between 0.05 and 10.0weight percent of the total foamable polymeric mixture.
 8. The foamablepolymeric mixture of claim 1, wherein said processing aid ismicroencapsulated.
 9. The foamable polymeric mixture of claim 1, furtherincluding at least one infrared attenuating agent.
 10. A method ofmanufacturing extruded polymeric foam comprising: introducing a polymercomposition into a screw extruder to form a polymer melt; injecting atleast one organic phase changing processing aid and at least one blowingagent into said polymer melt to form an foamable polymeric material,said blowing agent comprising one or more of carbon dioxide,hydrofluorocarbon, and hydrofluoroolefin; and extruding said extrusioncomposition through a die under a processing temperature between 800 and1200° F. to produce a polymeric foam.
 11. The method of claim 10,further including the step of microencapsulating said processing aidinto a powder prior to injection into said polymer melt.
 12. The methodof claim 10, further including the step of compounding said processingaid into said polymeric composition forming a masterbatch.
 13. Themethod of claim 10, wherein said processing aid comprises at least oneof a fatty acid ester and a wax.
 14. The method of claim 10, whereinsaid polymeric foam is a substantially closed cell foam.
 15. The methodof claim 10, wherein said polymeric foam has an R value between about4.0 and 7.0.
 16. An extruded polymeric foam comprising: a foamablepolymeric material, said material comprising: a polymer composition; atleast one blowing agent, said blowing agent comprising at least one ofcarbon dioxide, hydrofluoroolefins, and hydrofluorocarbons, and mixturesthereof; and at least one processing aid comprising an organic phasechanging material, wherein said foam has an R-value between 4 and
 7. 17.The extruded polymeric foam of claim 16, wherein said polymercomposition comprises a polystyrene.
 18. The processing aid of claim 17,wherein said processing aid is compounded into said polystyrene forminga masterbatch.
 19. The extruded polymeric foam of claim 16, wherein saidprocessing aid is a fatty acid ester.
 20. The extruded polymeric foam ofclaim 16, wherein said processing aid is a synthetic beeswax.
 21. Theextruded polymeric foam of claim 16, wherein said processing aid ismicroencapsulated by a polymer material comprising one or more ofmelamine formaldehyde, urea formaldehyde, and acrylate copolymer resins.22. A foamable polymeric mixture comprising: a polymer composition; atleast one blowing agent, said blowing agent comprising at least one ofcarbon dioxide, hydrofluoroolefins, and hydrofluorocarbons, and mixturesthereof; and at least one processing aid comprising an organic phasechanging material, wherein said foamable polymeric mixture is capable offorming an extruded polymeric foam, said foam having: an R-value between4 and 7 per inch; an average cell size between 0.005 and 0.6 mm; acompressive strength between 6 and 80 psi; a density between 1.3-4 pcf;and an open cell content of less than 30 percent.
 23. The foamablepolymeric mixture of claim 22, wherein said extruded polymeric foam hasa an open cell content of less than 10 percent.
 24. The foamablepolymeric mixture of claim 22, wherein said foamable mixture is capableof forming said extruded polymeric foam at a pressure range of 800 to1200 psi (5.5 to 8.3 MPa).